In ink-jet printing methods, droplets of ink are directly projected onto a printing medium from very fine nozzles and allowed to adhere to the printing medium to form characters or images thereon. The ink-jet printing methods have now been extensively employed not only in printing applications for ordinary consumers but also recently in commercial and industrial printing applications because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the printing medium, non-contact with printed characters or images, etc.
In the commercial and industrial printing applications, for example, there has been proposed a high-speed printing method in which a rolled synthetic resin film is scanned using a stationary printing head of a line printing type.
In the high-speed printing using a resin printing medium, since it is needed to conduct the work for taking up the printing medium, there is an increasing demand for quick-drying technologies for drying an ink used therein. As the quick-drying technologies for printed materials, an infrared drying system capable of drying the printed materials with a high energy immediately after being printed is considered to be effective. However, when irradiating portions of characters or images formed by color inks with infrared rays, owing to the difference between infrared absorption amounts of a yellow ink, a magenta ink, a cyan ink and a black ink among the color inks, a temperature difference tends to be caused on a surface of the printing medium, in particular, the portion of the printing medium which is printed by the black ink tends to be heated to an elevated temperature, so that there tends to occur such a problem that the printing medium suffers from thermal deformation.
Under these circumstances, there have been proposed printing apparatuses that are equipped with a means for accelerating drying of a printing medium.
JP 2010-137519A (Patent Literature 1) discloses an image-forming apparatus that includes a printing head for ejecting droplets of a liquid, a transportation means for transporting a printing medium in an opposed relation to the printing head, and a means for bringing a superheated steam into contact with the printing medium on at least one of an upstream side and a downstream side of the printing head in a transporting direction of the printing medium.
JP 2010-158861A (Patent Literature 2) discloses a printing apparatus such as an ink-jet printer which includes a printing means for performing printing onto a printing medium, a transportation means for transporting the printing medium, and a drying means for emitting a superheated steam to the printing medium to accelerate drying of the printing medium.